Table 1. The Factors and Their Levels 表1 试验各影响因素取值范围及实验分组
Factor 影响因素 Addition of resin
树脂加入量（%) Addition of curing
固化剂加入量（%） Total acid content of curing agent
固化剂总酸度（%） Sand temperature
砂温（℃） AFS grain size
型砂粒度（AFS细度） Ash content
灰分（%） Ambient temperature
环境温度（℃） Ambient humidity
环境湿度（%）
Experimental Design Because a lot of factors affect the work time and
tensile strength of molding sand, just some factors were selected for testing, including the amount of resin added, the amount of curing agent, the total acid content of the curing agent, sand temperature, molding sand grain size (average fineness), ash, ambient temperature, and ambient humidity. (Ash effect was not considered for work time, and sand temperature and the total acid content of the curing agent were not considered for the tensile strength test.) Each factor was classified into five levels as listed in Table 1. Te all-factor orthogonal experimental design was used. Te acidity of curing agent is achieved by controlling the
proportion of a curing agent with high acid value and one with low acid value. Te grain size of regenerated sand, sand temperature, ambient temperature and ambient humidity are test factors. Teir actual values are measured.
Test Method Empirical judgment was applied to determine the work
time, i.e., the time from the end of sand mixing to when the sand starts to be sticky but still has good flowability. Te judgment depends on the operator, so only one person was involved in the judgment, to reduce error due to human factors. Preparation of the specimen and the test of its tensile
strength was in accordance with Chinese industrial standard for self-hardening furan resin for castings (JB / T 7526-2008). Te test coupon for tensile strength was placed in a chamber with constant temperature and humidity for hardening.
Results and Discussion Te work time results and factors such as the molding
sand grain size, resin addition, curing agent addition, sand temperature, total acid content of the curing agent, ambi- ent temperature and humidity were analyzed by Minitab. Te regression analysis results are listed in Table 2. Te multivariate functional relationship between the work time and factors is:
MPa, 粘度20 mPa•s左右(25 ℃), 游离甲醛≤0.3%; （3 ）高酸值固化剂（总酸度31%～34%, 密度1.1～1.2 g/ cm3）; 低酸值固化剂（总酸度6%～8%, 密度0.9～1.0 g/cm3）。
1.2 试验设计
由于可使用时间和抗拉强度影响因素很多, 若全面考 虑试验量太大, 因此试验只选择树脂加入量、固化剂加 入量、固化剂总酸度、砂温、型砂粒度（平均细度）、 灰分、环境温度、环境湿度（其中可使用时间未考虑灰 分影响, 抗拉强度未考虑砂温和固化剂总酸度影响）做 为试验的影响因素, 每个因素各设置5个水平, 采用全因 子正交实验法进行实验设计。试验各影响因素取值范围 及分组如表1所示。
说明: 不同总酸度的固化剂是由高酸值固化剂和低酸 值固化剂按照不同比例配制而成; 再生砂粒度分组值、 砂温、环境温度、环境湿度为试验设计值, 具体记录以 实际测定值为准。
1.3 试验方法
试验采用经验判断法来判定可使用时间, 即从混砂结 束开始计时, 至型砂发粘但具有较好流动性的这段时间 记为可使用时间。由于不同人感觉可使用时间有所差异, 所以试验中可使用时间的判定均由一人完成, 以减少由 于人为因素带来的误差。
抗拉强度试样的制作及强度测定按照铸造用中华人民 共和国自硬呋喃树脂行业标准（JB/T 7526—2008）的 方法进行。做好的抗拉试块放置在设置好温湿度的恒温 恒湿箱中硬化。
2 结果与讨论 2.1可使用时间数据处理
利用Minitab软件对可使用时间与型砂粒度、 树脂 February 2013
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 59 0-40 30-90 0, 10, 20, 30, 40 30, 45, 60, 75, 90 Range
取值范围 0.7-1.2
20-60
（占树脂） 6-34
0-40 20-50 0-2.5 Levels 实验分组 0.7, 0.8, 0.9, 1.0, 1.1 20, 30, 40, 50, 60 12.8, 17.6, 22.4, 27.2, 32 0, 10, 20, 30, 40 20, 30, 40, 50, 60 0, 0.5, 1, 1.5, 2
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